1. Field of the Invention:
The present invention relates to a thermoplastic resin composition comprising a major amount of a rubber-modified styrene thermoplastic resin, a small amount of an aromatic polyester with a specific intrinsic viscosity, and a small amount of an aromatic polycarbonate. The thermoplastic resin composition possesses a high impact resistance and provides a painted surface with a superior appearance when a paint is applied on its surface.
2. Description of the Background Art
A rubber modified styrene thermoplastic resin is light in weight and can excellently be processed or molded. A secondary processing such as painting and galvanization can easily be applied to the molded surface. Because of these reasons, the resin is abundantly used for bodies or chassis of automobiles and the like. A rubber modified styrene thermoplastic resin, however, is unstable against organic solvents used for paints and produces deficiencies on the painted surfaces after finishing, such as crazing and very fine cracks leading to lack of glossiness, due to residual stresses created during the molding.
A method known in the art to solve the problem and to improve the external appearance of the painted surfaces is to use a large amount of monomers having polar groups, e.g. cyano compounds, for producing rubber modified styrene thermoplastic resins. Even though the method can improve the external appearance of the painted surfaces, moldability, processability, and molding heat stability of the resin are greatly impaired. Adhesion of the painted film to the substrate also decreases.
Thus, the improvement in external appearances of the painted surfaces involved the problem of worsening the intrinsic properties of the resin, such as superior moldability, processability, heat stability, and the like. They are inherently incompatible with each other. Conventional technologies could not find an adequate solution to the problem.
The present inventors have undertaken extensive studies in order to solve this problem, and found that incorporation of a small amount of aromatic polyester with a specific intrinsic viscosity and an aromatic polycarbonate could improve both the painted surface appearance and the impact resistance of a rubber modified styrene thermoplastic resin.